LEDs have recently been attracting attention and widely used as a light source in a lighting device mounted on a dental handpiece for their lower electric power consumption and longer service life compared to conventional halogen lamps. JP-10-137263-A discloses a light-emitting device which includes an LED enclosed in a translucent cover, and electrode terminals electrically connected to and linearly extending from the LED, and is in a compact size as a whole suitable for installation in a dental handpiece. The translucent cover enclosing the LED is in the form of a bullet, out of which the two linear terminals (anode and cathode terminals) connected to the LED extend. The light-emitting device is installed in a dental handpiece with the two linear terminals being connected to the connecting terminals of a lighting device arranged in a coupling connecting a handpiece body and a hose. In the installed state, the light-emitting device is arranged facing to the light-receiving surface of the optical fibers disposed in the handpiece body to introduce light emitted from the LED into the optical fibers.
However, in such a conventional light-emitting device, the LED is inevitably arranged apart from the light-projecting surface of the translucent cover facing to the LED, due to the bullet shape of the cover and the semispherical shape of the light-projecting surface. Accordingly, the distance from the light-emitting part of the LED to the semispherical light-projecting surface is added to the distance between the light-emitting part of the LED and the light-receiving surface of the optical fibers. The light emitted from the LED is scattered between the light-emitting part of the LED and the semispherical light-projecting surface, and is not efficiently introduced into the light-receiving surface of the optical fibers. This reduces the amount of light entering the optical fibers to lower the intensity of illumination (brightness) and causes color shading.